Probabilistic Shaping for Peak Power Constrained IM-DD Optical Fiber Communication Systems: Perspective of Envelope Control

Probabilistic shaping (PS) has attracted significant attention in intensity-modulation and direct-detection (IM-DD) optical fiber communication systems. Nevertheless, owing to the unique system model and inherent limitations, the practical applicability of the PS technique in IM-DD systems remains an open question, particularly in scenarios involving system memory. In this paper, diverging from the conventional PS technique, a novel indirect PS scheme tailored for practical peak power constrained (PPC) IM-DD optical fiber communication systems is proposed by taking the system memory into consideration. The key idea lies in strategically controlling the signal envelope to mitigate system memory-induced direct and indirect impairments, such as peak-to-average power ratio enhancement, overshoot, and nonlinearity distortions. The proposed scheme incorporates a dynamic selective mapping (DSLM) mechanism at the transmitter, enabling an untypical bit-to-symbol mapping rule in which the current symbol is not only determined by the current bit sequence but also by previously generated symbols within a specified memory length. At the receiver side, a modified turbo equalizer is proposed to achieve the recovery of ambiguous bits induced by DSLM. Experimental verification in a 56GBaud 8-ary pulse amplitude modulation (PAM8) system demonstrates that the proposed scheme exhibits 1 dB receiver sensitivity improvement over 2 km single-mode fiber transmission. In addition, the proposed scheme has also been demonstrated to be compatible with the typical probabilistic amplitude shaping architecture, enabling a simple and fine-granularity rate adaptation capability. To the best of our knowledge, this work opens a new sight for the application of PS technique in PPC IM-DD systems with memory.